Wood gasifiers can power either spark ignition engines where
100% of the normal petrol can be replaced with little change to
the carburation, or in a diesel engine by simply feeding the gas
into the air inlet when the diesel governor automatically cuts
back the diesel to fuel to between 15% - 40%. In the latter case
the diesel fuel is still needed to ignite the gas. Wood can be
used to power cars with ordinary internal combustion engines if
a wood gasifier is attached. This was quite popular during World
War II in several European and Asian countries because the war
prevented easy and cost-effective access to oil. In more recent
times, wood gas has been suggested as a clean and efficient method
to heat and cook in developing countries, or even to produce electricity
when combined with a gas turbine or internal combustion engine.
Compared to the WWII technology, gasifiers have become less dependent
on constant attention due to the use of sophisticated electronic
control systems, but it remains difficult to get clean gas from
them. Purification of the gas and feeding it into the natural
gas pipelines is one variant to link it to existing refueling
infrastructure. Liquification by the Fischer-Tropsch process is
another possibility.

Efficiency rate of the gasifier system is relatively high.
The gasification stage converts about 75% of fuel energy content
into a combustible gas that can be used as fuel for internal combustion
engines. Based on long term practical experiments and over 100
000 km driven with wood gas powered car, the energy consumption
has been 1.54 times more compared to the energy demand of the
same car on petrol (not including the energy needed to extract,
transport and refine the oil from which petrol is derived). This
means that 1000 kg of wood combustible matter has been found to
substitute 365 litres of petrol during real transportation in
similar driving conditions and with the same otherwise unmodified
vehicle [2]. This can be considered to be a good result, because
no other refining of the fuel is required. This study also considers
all possible losses of the wood gas system like preheating of
the system and carrying of the extra weight of the gas generating
system.

Gasifiers have been built for remote Asian communities using
rice husk, which in many cases has no other use. One installation
in Burma uses an 80kW modified diesel for about 500 people who
are otherwise without power.[3] The ash can be used as fertilizer
so this can be considered a renewable fuel. It has been suggested
that the rice husk ash, which is particularly pure and high in
silica can be used at high economic value in e.g. semiconductor
manufacture.

Against general belief, exhaust gas emission level of internal
combustion engine is significantly lower on wood gas than on petrol.
Especially low are HC emissions. A normal catalytic converter
works well with wood gas but even without it, emission level less
than 20 ppm HC and 0,2 % CO can be easily achieved by most automobile
engines. Combustion of wood gas generates no particulates and
the gas thus renders very little carbon black amongst motor oil.